Sara was great too, yes more range but so did a lot of opera singers. but she didn’t go into all the kinds of music Ella did.
Sara's voice has been described as having a "large vocal range of soprano through a female baritone, exceptional body, volume, and a variety of vocal textures".
Personally, the timbre of Vaughan's "burnished contralto" was more appealing to me. However, I regard them as equals; and they were always very complimentary of each other.